Résumé

Magnetic Evolution of Neutron Stars towards the Hall Attractor

Konstantinos Gourgouliatos (McGill University )

Andrew Cumming (McGill University)

The evolution of the magnetic field of neutron stars in their crusts is dominated by the Hall effect and ohmic dissipation. While cartesian box simulations of the Hall effect suggest that the magnetic field undergoes turbulent cascade and dissipates, observations of middle aged neutron stars confirm that they still host magnetic fields that has not suffered significant dissipation. We address this issue by performing simulations of the Hall effect and ohmic dissipation in neutron star crusts, which include the density and conductivity structure of a realistic crust. We find that after some early response of the magnetic field to the initial conditions chosen, the Hall evolution saturates and the field relaxes to a Hall attractor. This attractor state is reached for a great variety of initial conditions chosen and corresponds to isorotation of the electron fluid on surfaces of constant magnetic flux similar to Ferraro's law for magnetohydrodynamics. The field consists mainly of a dipole and octupole component with a weaker toroidal dipole, and we propose that such a field can be a realistic description of the magnetic structure of middle aged neutron stars.